1. Field of the Invention
The invention concerns a technique to output fonts on high resolution output devices.
2. Prior Art
High resolution output devices include, for example, electronic phototypesetters or high resolution laser printers. These devices include a separate processor unit which receives the text as such to be output, for example from an external computer, and with the application of digitally stored fonts converts it into a pre-set font form of a particular font type and size. A margin adjustment can also be taken into consideration in this process. The data output by the separate processor unit contains complete information about the font image and is fed to an interim storage, which serves to activate an output unit which transfers the data, for example with the help of a laser beam, onto a duplicating medium such as a film or paper.
Font size is measured in a typographic unit, which is denoted with point (pt), and it is: 1 pt=0.351 mm (Europe: 0.375 mm). In the past all the different point sizes of a font were specially manufactured. The stamp punch of the letters was created by hand and served for the production of the matrixes. With this the letter image could be transferred by the typesetter into lines of poured lead. Later, in addition to this hot metal technique photocomposition appeared, which made the enlargement or reduction of letters in a linear fashion possible. With this development, one only needed to produce a font in one size as a master (normal size or design size) and could create various desired font sizes through linear scaling in the photocomposition machine. This method, to simply manufacture one master, spread generally throughout the graphic industry for cost reasons.
In the last few years the photocomposition technique has been superseded by computer-controlled phototypesetting techniques. The typefaces are stored digitally, and in this context outline coding has caught on extensively today, in which the contours or edges of a letter are described through discrete control points and connected curve elements as displayed in FIG. 1. For example the X-, Y-co-ordinates of the start, corner, curve and tangent points are digitized as points and the curve elements are described as a set of vectors, as arcs of circles, as Bezier-functions, as spirals or as Spline-functions by the various manufacturers. An overview of the digital font formats can be found in the book "Digital Typefaces", Peter Karow, Springer Verlag, Berlin Heidelberg, 1992 (hereby incorporated by reference). Even with digitally stored fonts, today a simple master is used for each font type, and this is re-scaled according to the desired size, both for low resolution printers as well as for high resolution phototypesetters. A low resolution runs, for example, to 100 lines per inch (lines per inch=lpi) in the case of screen devices and up to 300 lpi with dot-matrix or laser printers. The high resolution runs to around 2500 lpi with electronic phototypesetting systems. This means, for example, that fonts on screens in 9 pt text size have a stroke width of only one screen point (pixel), whereas on the other hand with high resolution the same stroke width is formed from 25 pixels.
Aside from the control points for definition of the outline, the letters receive so-called instructions which are used for the rasterization to output the letter, for example on a laser printer or a screen, and is used today by all manufacturers of digital fonts to "intelligently raster" (Intelligent Font Scaling) (compare, e.g., "Intelligent Font Scaling" by Peter Karow, URW brochure, or Peter Karow "Intelligent Font Scaling--The Technique of Sizing Fonts", Hamburger Satzspiegel, Hamburg 3/1990) (hereby incorporated by reference).
The linear re-scaling of digitally stored fonts as applied previously is, however, still unsatisfactory in various aspects. The font sizes manufactured from a master through linear enlargement/reduction are at the moment clearly inferior in their legibility and entire aesthetic impression to the optically correct and typographically appropriately manufactured font sizes. The typographically correct "Optical Scaling", as applied without further thought or rules for the separate production of font sizes during the days of hot-metal, takes into consideration that the resolving power of human eyes is limited. We need a larger interval between letters for small printed text (e.g. 5 pt) than for normal book text (e.g. 9 pt), in order that the letters do not seem to grow together and the small text remains readable. The same applies for small white inner counters such as in the lower case letter e. Very thin strokes (e.g. swash lines, so-called hair lines) must be strengthened with small font sizes, in order that they remain at all recognizable and don't "break through", i.e. partly disappear during the printing process. Conversely, if one proceeds to bigger inscriptions (advertising, placards, titles), the letters throughout can be placed relatively closely together, inner counters can remain small and hair lines thin. This allows, if one starts from a master in the design size of the font, a summary in approximately the following way:
The smaller the font size,
1) the wider the setting, PA1 2) the broader the letters, and PA1 3) the thicker the strokes. PA1 1) the narrower the setting, PA1 2) the letters can be narrower and PA1 3) especially the hair lines can be finer. PA1 (a) supply a single master font in a digitized outline coding, in which the contours of each letter are provided with delimiting discrete control points and additionally with instructions, such as those stipulated for the "Intelligent Font Scaling", PA1 (b) linearly re-scale the master font with a factor to the desired point size, PA1 (c) apply the instructions according to the invention at issue in order to continuously vary the stroke width of the linearly re-scaled letters with the factor in a pre-set factor dependency, wherein the stroke width is increased for factors less than 1 and is decreased for factors larger than 1. PA1 (a) supply a single master font in a digitized outline coding, in which the contours for each letter are provided with delimiting discrete control points and additionally with instructions, such as those stipulated for the "Intelligent Font Scaling", PA1 (b) linear expansion or condensation of the master font with a factor to the desired width, PA1 (c) apply the instructions according to the invention at issue in order to hold the stroke width constant during expansion or condensation of letters, to thereby only make the inner counters wider or narrower.
The bigger the font size,
Until now there have only been a few attempts at optical scaling of digitally stored fonts. In the year 1990 Henry Schneiker from the firm Kingsley/ATF, Tucson, Ariz., held a lecture at the Rochester Institute of Technology on "Type Quality vs. Type Technology". He suggested digitizing fonts and then to apply the concept of "Optical Scaling", used by ATF for lead, interactively on the screen for the digital fonts as well. Thereby he starts from the perspective that--although computer aided--the creation is still, as in the past, handwork.
In March 1991 the firm Adobe Systems, California, announced a concept called "Multiple Master". In connection therewith an automatic technique for optical scaling is displayed and explained for the first time. Two master fonts are necessary, one in a very small point size, and the other in a very large point size. The point sizes lying in-between are calculated through mathematical interpolation.
Further, for a typographically correct setting the problem of expansion/condensation (widening/narrowing) plays a role. Up until the discovery of the photocomposition technique, this requirement for print type in machine typesetting could only be satisfied through the offer of expanded or respectively condensed fonts. These broader, or respectively narrower variations of a print type had to be produced through expensive hand work. Therefore for cost reasons they were not manufactured and made available for most fonts. With the modern photocomposition technique the problem of expansion/condensation was solved with help from cylindrical mirrors or respectively lenses. In the same way electronic phototypesetters, discovered somewhat later, handled this problem through simple linear widening and narrowing of the letters. Thereby the letters in their entirety, i.e. both the black letter strokes as well as the white inner counters in the letters and between the letters in the typeset word would be widened or respectively narrowed.
With the IKARUS-System the firm URW has pursued a technique since 1975, by which the letters can be typographically correctly expanded/condensed half automatically. With help from protection zones the IKARUS-System is informed which vertical areas of a letter to hold rigid and which are variable with respect to their width. This technique does not allow itself to be fully automated, there always remains a residue of screen work for the font designer. Since 1981 the firm URW has started to apply the technique of linear mathematical interpolation for the purpose of condensation/expansion.
In the same way, with the concept of "Multiple Masters" interpolation for the purpose of automatic expansion/condensation is employed by the firm Adobe Systems, California. Thereby two fonts as master are always necessary, a narrow (condensed) one and a wide (expanded) one. This has the grave disadvantage that, not only is double the work necessary to manufacture the font, but also double the storage space is needed for fonts in the phototypesetters.
In newspapers and books text is normally made available "justified", which means all lines have the length of the column-width for columns. First of all the text is produced ragged, as shown in FIG. 15. Traditionally the interword space is then widened so that the lines, as in FIG. 16, are of the same length. This has the disadvantage that big gaps between words arise repeatedly, which impede the flow of reading. The technique of automatic linear expansion/condensation can likewise be applied, but leads to apparently emphasized (expanded=spaced out) or respectively insignificant (condensed=narrow printed) spots in the text, as is clear from FIG. 17, for which reason this technique is hardly used. One can overcome this disadvantage through correctly expanding or respectively condensing the letters typographically. Thereby, in keeping with FIG. 18, only the inner counters but not the stroke widths may be altered. If justifying is carried out with letter text expanded/condensed in such a way, effects of oversized gaps or unwanted accentuations no longer appear, as is recognizable from FIG. 19, instead a typographically desired solution for exacting column typesetting arises.